RECENT DEVELOPMENTS IN EDUCATION 409 work was done, as he put it himself, with only " a pen, a piece of paper, and much patience." On a fortunate day for education he was invited by the French Minister of Public Instruction to act on a commission dealing with the question of feeble-minded children, and he set himself with ardour to the discovery of a scientific criterion of backwardness. The plan followed by him in his inquiries was to think out a large number of tests of varying difficulty which would be at once speedy and precise, to try out the tests with a great many normal children, and to construct a scale of tests with those which proved successful at particular ages. Out of the investigation, carried on in collaboration with Dr. Simon, came the Binet-Simon Tests. The version published in 1905 consisted of 30 tests; the second in 1908 of 56 tests, arranged according to age, for children form 3 to 13: the final revision in 1911, made just before his death, had five tests for each year from 3 to 10 and a like number for 12 and 15. The secret of the success of the Binet Tests is to be found in the two assumptions on which they were constructed. The first was that it is possible to measure the amount of a person's in- telligence. Before Binet's time the study of the individual mind had made little progress. Previous investigators had set them- selves to define the difference between individuals in terms of specific abilities, but in spite of the fact that there really are important differences in such abilities they had failed to give any account of mind capable of simple practical application. Binet changed the situation by concentrating attention on intelligence and converting the problem from a qualitative to a quantitative form. The question now came to be not what kind of mind a person had, but how much of the power called intelligence he possessed. The second assumption of the Binet tests was that every year in childhood sees a definite increase in intelligence capable of being determined by a consideration of the perform* ances of the average child in successive years. The tests for each year were simple measurable acts which experiment had shown to be exactly within the powers of the average child of that age. Instead of attempting to define age differences in general terms Binet said in effect: " Here is what the normal child of this age and that can do. Judge the individual child's intelligence by comparing his age calculated on the basis of his test performances with his actual age."